Sweetening of thermally cracked naphthas with alkali phenolate oxygen and sulfur



March 20, 1956 M. GORDON ET AL SWEETENING OF THERMALLY CRACKED NAPHTHASWITH ALKALI PHENOLATE OXYGEN AND SULFUR Filed June 26, 1955 IN V EN TORS1 Moses Gordan George E. Thompson ATTOI? Y United States PatentSWEETENING 0F THERMALLY CRACKED NAPH- THAS WITH ALKALK PHENULATE OXYGENAND SULFUR Moses Gordon and George E. Thompson, Chicago, 111., asslgnorsto Standard Gil Company, Chicago, Ill., a corporation of IndianaApplication June 26, 1953, Seriai No. 364,234

11 Claims. (Cl. 196-2?) 7 This invention relates to the sweetening ofsour thermally cracked naphthas. More particularly the invention relatesto the sweetening of thermally cracked naphthas having ASTM end pointsof not more than about 425 F. and mercaptan numbers of more than about1.2.

Virtually all naphthas derived from the distillation of crude petroleumor from cracking of petroleum fractions contain objectionable amounts ofmercaptans. mercaptain-containing naphthas are commercially spoken of asbeing sour. A naphtha which has been treated to remove substantially allthese mercaptans is known as sweet or doctor sweet. In the petroleumindustry a sweet oil is one which gives a negative doctor test. A morequantitative description of a sweet naphtha is one which has a so-calledmercaptan number or copper number of substantially less than 1, e. g.,about 0.5. Mercaptan number and copper number are defined as the numberof milligrams of mercaptan-sulfur per 100 milliliters of naphtha. Manyprocesses of sweetening naphthas are known. U. S. 2,015,038 teaches aprocedure wherein the sour naphtha is contacted with an aqueous causticsolution, phenolic compounds, and a free-oxygencontaining gas.(Satisfactory phenolic compounds for use in this process may be obtainedby caustic extraction of naphthas.) However, very surprisingly, it hasbeen found that thermally cracked napthas having a mercaptan Such numberhigher than about 1.2 are not sweetened by the process of U. S.2,015,038.

Another procedure for sweetening sour naphthas is to contact the sournaphtha with aqueous caustic and freesulfur. While this method isrelatively effective on virtually all stocks, it has been found to havea very serious disability, namely, the sweet naphtha almost alwayscontains corrosive sulfur. It is very difficult to control the sulfuraddition to just the amount needed for sweetening. When using thisprocedure the excess free-sulfur appears as corrosive sulfur in theproduct naphtha. Furthermore, since the sulfur must do all the oxidizingof-the agent.

mercaptaus to disulfides, a large amount of sulfur is re- 7 quired andthe product naphtha has a poor vtetraethyl lead susceptibility. e

It is an object of this-invention to sweeten sour therwill'becomeapparent in the course of the detailed de;

scription thereof. v

It has been discovered that thermally cracked naphthas having mercaptannumbers of more than about 1.2can be sweetened by the process whereinthe naphtha is contacted with an aqueous alkaline treating agent,preferably containing at least about 5 weight percent of free-caustic,which contains at least a catalytic amount and preferably at least about2 volume percent of alkylphenols, freeoxygen, and at least an amount offree-sulfur effective to sweeten said feed but not enough to produce acorrosive naphtha product. The contacting is carried out at atemperature of at least about F., preferablyat between about F., and F.,for a time sufiicient to give a product which is doctor sweet, i. e., amercaptan number substantially less than 1, e. g., 0.5-0.7.

The feed to this process is naphtha derived from thermal cracking. Bythermal cracking is meant petroleum refinery operations such asvis-breaking, coking, gas oil cracking, heavy naphtha reforming, etc.cracked naphtha feed has an ASTM end point of not more than about 425 F.and preferably has a boiling range between about 120 F. and 400 F. Thenaphtha feed may be prewashed with a weak caustic solution to removeHzS, but it is not essential that the feed be HzS-free. A thermallycracked naphtha which has been subjected to a conventionalcaustic-cresylate extraction process to remove a portion of themercaptans is also a satisfactory feed for this process.

The feed to this process should have a mercaptan number of more thanabout 1.2; although lower mercaptan content naphthas may be charged tothe process. Naphthas with a mercaptan number in excess of about 20 maybe sweetened by this process, but preferably the mercaptan numbers ofthese naphthas should be reduced by other methods to about 20 or less.

The aqueous treating agent used in this process is present in an amountat least sufiicient to form a separate phase. sweetening can be obtainedwith amounts of agent just great enough to impart a haze to the naphtha.For most operations the amount of the aqueous treating agent will beabout 10 to about 200 volume percent based on the feed naphtha. It ispreferred to use about 25% to about 50% by volume of aqueous treatingagent in this process.

The caustic component of the aqueous treating agent may be sodiumhydroxide, potassium hydroxide, or mixtures thereof. The caustic ispresent in the treating agent in the form of free-alkali and in chemicalcombination with the alkylphenols. Furthermore, some of the caustic maybe combined with acidic contaminants in the treating Free caustic mustbe present, preferably, at least about 5 weight percent. Higherconcentrations of caustic may be used and in some cases a saturatedsolution may be desirable, e. g., about 50% of NaOH. It is preferredthat the total caustic content, i. e., free and combined caustic, of theaqueous treating agent be between about 15 and 25 weight percent.

The alkylphenols used in this invention may be any .alkylhydroxybenzene,such as cresol, xylenol, etc. The

7 rived from thermal cracking and catalytic cracking processes. Thesealkylphenols may be obtained by contacting the petroleum hydrocarbonwith concentrated aqueous caustic solution. The cresols derived fromcracked naphtha have an ASTM boiling range from about 370 F. to about440 F. Alkylphenols occur in petroleum hydrocarbons boiling in theheavier-than-gasoline range, i. e., hydrocarbons boiling from about 350F. to about 600 F. These alkylphenols are usually called heavy xylenolsand may be obtained by contacting cracked gas oils and many virgin gasoils with concentrated aqueous caustic solution such as a 40% solution.These heavy xylenols have an ASTM boiling range between about 375 F. and560 F. or higher.

The alkylphenols present in the aqueous treating agent act as solutizersfor the mercaptans. The alkylphenols The thermally also aid inpreventing the presence of corrosive sulfur in V the naphtha, and it ispossible that they do this by reacting with the excess free-sulfur. Itis necessary to have at least a catalytic amount of alkylphenols presentin the ll. of light ends, i. e., butanes and pentanes, to avoidsubstantial losses of these by evaporation during the processing. It isdesirable to use higher temperatures as the sweetening reaction isaccelerated by higher temperatures.

aqueous treating agent, and preferably at least about 2 5 Therefore, forthermal naphtha feeds boiling between volume percent. It is advantageousto have more alkylabout 120 F. and 400 F, temperatures of about 120 F.phenols present and in some cases a saturated solution to about 160 F.are preferred. For naphthas which are may be desirable. However, thesealkylphenols increase more refractory, i. e., harder to sweeten,temperatures the viscosity of the agent and may produce phaseseparaabove 160 F. may be used. tion difiiculties. It may be desirableto limit the alkyl- The mixture of free-sulfur, agent, naphtha andfreephenols to about 30 volume percent when using sodium oxygen shouldbe maintained intermingled for a time sufhydroxide, preferably about 20;somewhat higher amounts ficient to complete the sweetening reaction, i.e., to promay be used when using potassium hydroxide. It is duce anaphtha having a mercaptan number substantially preferred to use betweenabout 5 and 20 volume percent less than 1. The required contacting timeis dependent alkylphenols in the aqueous treating agent. on themercaptan number and the type of naphtha, but The free-oxygen may beintroduced into the process normally this time will be between about 1minute and either in the form of substantially pure oxygen, i. e., 60minutes. For most feeds, a contact time of from cylinder oxygen, or inthe form of a free-oxygen-conabout 2 to about minutes will besufficient. taining gas, e. g., air. Very slight amounts of free-oxygenAfter the completion of the sweetening reaction the are needed tooxidize the mercaptans in the naphtha to 20 mixture of treating agentand naphtha is settled for a time disulfides, but at least an amountsufiicient to oxidize the sufiicient to separate the product naphthafrom the lower easily oxidizable mercaptaus is desirable since thesulfur aqueous phase. The aqueous phase is usually suitable isparticularly required for the oxidation of mercaptans for recycle to theinitial contacting step. However, in which are difiicult to oxidize. Theamount of free-oxygen the course of time there is a buildup ofthiosulfates and required will increase with increasing mercaptan numberother by-product salts which interfere with the sweetenof the sournaphtha. Usually 5 s. c. f. of air will be sufing process and reduce thefree-caustic concentration. ficient for the production of a sweetproduct. It is pre- The cresols also build up in the treating agent,when the ferred to add between about 0.2 and 2 standard cubic naphthafeed has not been prewashed with caustic to refeet of free-oxygen perbarrel of sour naphtha. When move HzS or extracted withcaustic-cresylate solution air is used, from about 1 to about 10 s. c.f. of air are for mercaptan number reduction. It is therefore desirableadded per barrel of sour naphtha. to periodically discard the treatingsolution and use fresh It has been found that thermally cracked naphthashavsolution; or to continuously withdraw a portion of the ing mercaptannumbers greater than about 1.2 cannot be treating agent and replace itwith fresh solution. sweetened by contacting the naphtha with an aqueousThe results obtainable by the process of the invention caustic-cresolsolution in the presence of air even at are illustrated by a number oflaboratory experiments. elevated temperatures and for prolongedcontacting time. Naphthas for the laboratory experiments were mercaptan-It has been discovered that a sweet product can be obextracted usingconventional caustic-cresylate extraction tained by operating in thepresence of free-sulfur. The to various mercaptan numbers from 1.0 to4.1. Sweetenamount of free-sulfur must be at least an effective amounting of these naphthas was carried out using both the but less than theam unt whi h giv s a C rr pro 40 canstic-cresylate-air-sulfur method ofsweetening and the p The use of free-Sulfur afificts favorably thecaustic-cresylate-air method for comparison. The temcontactingtemperature and contacting time. The amount perature at which all runswere conducted was 140 F. of free-sulfur requu'edincreases withincreasing mercaptan The strength of the caustic solution used in theexperi number of the naphtha i of more than about ments-varied fromabout 19 to 22 weight per cent based has?safest.22:1.a;zlisfsae sjzaszzon the In effect on the TEL Susceptibility of product naphtha, ofnaphtha and 100ml. of caustwcresylate solution were and a corrosivenaphtha product may result. Amounts used In an runs i i added f therate, i i we of free-sulfur as low as 0.5 lb./1000 bbls./mercaptan(standard condltlmfs) per mmute' Dlsnllfmogs P number or lower may besufficient with some naphthas. f the naphthas used the l f expenmentsPreferably, between about 0.9 to about 1.6 pounds of dlcated that theyall 1901164 Wlihln the range 0f sulfur per 1000 barrels of naphtha feedper mercapt to 400 F. Additional details of these runs and the resultsnumber of said feed is used to obtain a doctor sweet thereof areshowninTable I.

Table I Runs 1 2 a 4 5 a 7 FeedMercaptanNo 12-.-... 4.1.

Time, Minutes s s 20.

Vol. Percent Cresols, based 20 20 10 20.--" 20.

on Agent. Sulfur, mg. None None- 2.4 None None- None. 8.2. Product:Sweet... Sour- Sweet... B0rder1ine-. Sour.- Sour- Sweet.

1 Sulfur added in Runs 3 and 7 is equivalent to 1.8 lbs/1,000 bbls.naphtha/mercaptan number.

product with thermally cracked naphthas having a boiling range betweenabout 120 F. and 400 F. When the particular type of mercaptans presentin the naphtha are very difficult to oxidize, the amount of sulfurrequired to obtain a sweet naphtha product will correspond more closelyto the 1.6 figure than to the 0.9 figure; this is the case normally withnaphthas having ASTM end points appreciably above 400 F.

Normally, the practical extremes of temperature in which sweetening willbe carried out are from about 80 F. to 210 F. Temperatures below about100 F. are preferred for use on naphthas having substantial quantities Alarge 'scale embodiment of thisprocess is illustrated in theaccompanying drawing which forms a part of this specification. The,embodiment illustrated is schematic in nature; all pumps, valves, andmany other pieces of equipment have been omitted, as anyone skilled inthe art can readily add these items to the embodiment shown in thefigure.

Sour thermally cracked naphtha feed which has previously been extractedby conventional caustic-cresylate mercaptan extraction fi'oma mercaptannumber of 24 to a mercaptan number of about 7.5, and which has a boilingrange of between about 120 F. to 400 F. is charged from source 11 toline 12 at the rate of about 600 barrels per hour. All references rnadeto barrels in the description of the large scale embodiment refer to42-gallon barrels. From line 12 the naphtha flows to heat exchanger 13.Heated naphtha from exchanger 13 is passed by way of line 14 to line 15.i

Free-sulfur is introduced into the system by -means of naphtha, which ispreferably feed naphtha from source 11. This naphtha which containsabout 0.4 to about 0.5 weight percent sulfur and at a temperature ofabout 120 F., is fed at a rate of about 0.6 barrel per hour from source16 by way of line 17 to line 15. Free-sulfur may be metered directlyinto line 15 or dissolved in naphtha other than a portion of the feed.Normally adding the free-sulfur in solution in a portion of the naphthafeed is the most desirable method.

Air from source 18 is fed at a rate of about 2400 standard cubic feetper hour by way of line 19 to line 15.

Recycle aqueous caustic-cresylate solution, which may contain makeupfresh caustic-cresylate solution is fed from line 20 to line 15 at arate of about 150 barrels per hour. This aqueous solution has afree-caustic concentration of about 8 weight percent and a cresolconcentration of about 15 volume percent.

The naphtha, naphtha-containing free-sulfur, air, and :aqueouscaustic-cresylate solution mix together in line 15. Additional mixing ofthe components is provided by mixer 21. Mixer 21 may be any conventionalmixer, e. g., a knothole mixer.

Efiiuent from mixer 21 is fed by way of line 22 to contactor 23 at apoint near the bottom of contactor 23. Contactor 23 is a cylindricalvessel of about 400 barrels capacity. Its length is about 30 feet andits diameter about 10 feet, and it is installed in a vertical position.Contacting is carried out at about 120 F. for about minutes.

An aqueous phase is withdrawn by line 24 from the bottom of contactor23, either continuously or intermittently as desired. Naphtha containingsome of the treating agent both dissolved and suspended, in addition tothe air, is taken overhead from contactor 23 by way of line 25, andenters the second contactor 26 at a point near the bottom thereof.

Contactor 26 is a vessel of equal size and shape as contactor 23 and itis installed in a vertical position similar to contactor 23. Most of theaqueous phase carried into contactor 26 by the naphtha settles out inthe bottom of contactor 26 and is drawn oh" by line 27, eithercontinuously or intermittently as desired.

The naphtha efiluent from contactor 26 is fed by line 28 to settler 29.Settler 29 is a 400-barrel settler of the same size and shape as thecontactors 23 and 26. To obtain a haze-free product directly from theplant, it is necessary to use more than one settler of the size ofsettler 29, and it may be necessary to use as many as 3 or 4 suchsettlers in series. Conventional coalescers such as coalescers packedwith fibreglass or other suitably coalescing material may be used inplace of settlers to remove haze, or salt drums may be used in place ofsettlers to remove haze from the sweet naphtha product. However, if theplant eil'luent naphtha is to be pumped to storage, it can be settledfree of haze in the storage tanks and one settler is sufficient. It isalso possible that'no settlers" will be required and all the settlingcan be accomplished in storage.

The naphtha product, withdrawn by way of line 30, which is sweet andnoncorrosive, should be cooled to about ambient temperatures either byindirect heat exchange or by water washing. If direct cooling by waterwashing is used, a settler should be provided after the water wash stepto allow the water to settle free of the naphtha.

Substantially all the aqueous phase which has not settied out incontactors 23 and 26, settles out in settler 29. The aqueous layer whichsettles out as a bottom layer in settler 29 is withdrawn by line 31either continuously or intermittently as desired. a

The aqueous phase is withdrawn from the contactors and settler by lines24, 27 and 31 as previously indicated. Lines 24 and 31 feed into line 27to combine all the aqueous phases for recycle to mixer 21. Downstreamfrom the junction of lines 24, 27 and 31, a portion of the combinedaqueous phase may be withdrawn by way of line 32 either intermittentlyor continuously for discard as waste. Fresh caustic-cresylate solutionmay be added from source 33 by line 34either intermittently orcontinuously to fortify the recycle aqueous phase.

The air associated with the naphtha may be released at any time aftersweetening has been attained and normally it will be released to a ventline, but the air may be released in storage if proper safetyprecautions are taken. 4

Thus having described the invention, what is claimed is:

l. A process for sweetening a thermally cracked naph- V tha feed havinga mercaptan number of at least 1.2,

which process comprises contacting said feed, in the presence offree-oxygen, with an aqueous alkaline treating agent containing at leasta catalytic amount of alkylphenols, wherein said agent is present in anamount at least sufiicient to exceed the solubility of the agent in thefeed, and with an amount of free-sulfur at least efiective tosubstantially sweeten said feed but insuflicient to render the productnaphtha corrosive, at a temperature at least about F. for a time atleast sufiicient to produce a substantially sweet naphtha and separatinga substantially sweet, non-corrosive product naphtha from an aqueousphase.

2. The process of claim 1 wherein said agent is present in an amount atleast sufiicient to form a haze in said feed.

3. The process of claim 1 wherein said feed naphtha has an ASTM endpoint of not more than about 425 F. and a mercaptan number of not morethan about 20.

4. The process of claim 1 wherein said alkylphenols are present in saidagent in an amount of at least 2 volume percent.

5. The process of claim 1 wherein said free-sulfur is present in anamount of not more than 1.8 pounds per 1000 barrels of said feed permercaptan number of said feed.

6. The process of claim 1 wherein said temperature is between about F.and about F.

7'. A process for sweetening a thermally cracked naphtha feed having amercaptan number between at least 1.2 and 20, which process comprisescontacting said feed, in the presence of about 0.2 to about 2 standardcubic feet of free-oxygen per barrel of said feed, with an aqueoustreating agent, which contains at least about 5 weight percentfree-caustic and at least 2 volume percent alkylphenols, in amount ofbetween about 10 and 200 volume percent based on said feed, and withfree-sulfur in at least an amount effective to sweeten said feed but notmore than 1.8 pounds per 1000 barrels of said feed per mercaptan numberof said feed, at a temperature between about 100 F. and F. for a timesulficient to reduce the mercaptan number of said feed to substantiallyless than 1, and separating a sweet, noncorrosive product naphtha froman aqueous phase.

8. The process of claim 7 wherein said feed has an ASTM end point of notmore than about 425 F.

9. The process of claim 7 wherein said alkylphenols are derived from thethermally cracked naphtha feed.

10. A process for sweetening a thermally cracked naphtha feed having amercaptan number between at least 1.2 and 20, and an ASTM end point ofnot more than about 425 R, which process comprises contacting said feed,in the presence of about 1 to about 10 standard cubic feet of air perbarrel of said feed, with between about 25 and 50 volume percent basedon said feed of an aqueous treating agent which contains between about15 and about 25 weight percent of free and combined caustic and betweenabout 5 and about 20 volume percent of cresols derived irorn crackedpetroleum naphthas, and with frec-sulfur in an amount between about 0.9and 1.6 pounds per 1000 barrels of said feed per mercaptan number ofsaid feed, at a temperature between about 120 References Cited in thefile of this patent UNITED STATES PATENTS 1,767,356 Fischer June 24,1930 1,789,335 Fischer et a1. Jan. 20, 1931 2,143,405 Campbell et a1Jan. 10, 1939 2,638,439 Browder et a1 May 12, 1953 2,645,602 Torn et a1.July 14, 1953

1. A PROCESS FOR SWEETENING A THERMALLY CRACKED NAPHTHA FEED HAVING A MERCAPTAN NUMBER OF AT LEAST 1.2, WHICH PROCESS COMPRISES CONTACTING SAID FEED, IN THE PRESENCE OF FREE-OXYGEN, WITH AN AQUEOUS ALKALINE TREATING AGENT CONTAINING AT LEAST A CATALYTIC AMOUNT OF ALKYLPHENOLS, WHEREIN SAID AGENT IS PRESENT IN AN AMOUNT AT LEAST SUFFICIENT TO EXCEED THE SOLUBILITY OF THE AGENT IN THE FEED, AND WITH AN AMOUNT OF FREE-SULFUR AT LEAST EFFECTIVE TO SUBSTANTIALLY SWEETEN SAID FEED BUT INSUFFICIENT TO RENDER THE PRODUCT NAPHTHA CORROSIVE, AT A TEMPERATURE AT LEAST ABOUT 80* F. FOR A TIME AT LEAST SUFFICIENT TO PRODUCE A SUBSTANTIALLY SWEET NAPHTHA AND SEPARATING A SUBSTANTIALLY SWEET, NON-CORROSIVE PRODUCT NAPHTHA FROM AN AQUEOUS PHASE. 